Method of treating pancreatic and liver conditions by endoscopic-mediated (or laparoscopic-mediated) transplantation of stem cells into/onto bile duct walls of particular regions of the biliary tree

ABSTRACT

A method of repairing diseased or dysfunctional pancreas or liver is provided. The method involves preparation of a suspension of stem cells and/or progenitor cells such as biliary tree stem cells, hepatic stem cells, pancreatic stem cells or their descendants, committed progenitor cells, from healthy tissue of the patient or of the biliary tree of a non-autologous donor and engrafting the cells into the wall of bile ducts near to the organ to be treated. The graft consists of stem cells or progenitors that are admixed with biomaterials and, optionally, with cytokines and/or native epithelial-mesenchymal cells appropriate for the maturational lineage stage of the cells to be engrafted. The cells are specifically introduced to the hepato-pancreatic common duct of the subject for treatment of pancreatic conditions or to the bile duct wall near to the liver for treatment of liver conditions and allowed to migrate to the pancreas or to the liver and expand and then rebuild part or the entirety of the diseased or dysfunctional organ.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/780,644, filed Mar. 13, 2013, which is herein incorporated byreference it its entirety.

FIELD OF THE INVENTION

The present invention is directed generally to the field of cell-basedtherapies. More specifically, the invention concerns the cell-basedtherapies, particularly stem/progenitor cell therapies, for thetreatment of pancreatic and liver conditions. The determinedstem/progenitor cell populations can be biliary tree stem cells, hepaticstem cells, pancreatic stem cells, committed hepatic or pancreaticprogenitors, or mesenchymal stem cells. They might also be derivativesof embryonic stem (ES) cells or induced pluripotent stem (iPS) cells.

BACKGROUND OF THE INVENTION

Regenerative medicine has entered a new phase in which stem cellpopulations are being transplanted into patients to restore damaged ordiseased tissues such as liver and pancreas. Liver diseases, potentiallyleading to organ failure due to hepatitis viruses, alcohol consumption,diet and metabolic disorders, and other causes, constitute a majormedical burden world-wide. Similarly, pancreatic conditions,particularly diabetes, are a leading cause of health problems and deathworld-wide. Stem/progenitor cell therapies represent possible approachesto address these needs for treatment, and clinical programs areexpanding world-wide to explore these novel therapies further. Althoughmany types of precursors are being tested for clinical programs treatingliver and pancreas, only certain ones are possible for clinical programsin the near term.

Overview of Stem Cell Biology

The stem cells or their descendants, committed progenitors, are capableof both sustained proliferation and differentiation into specializedcells. The crucial defining distinction of stem cells is their abilityto self-renew, i.e., to maintain indefinitely a population withidentical properties, through either symmetric or asymmetric celldivisions. Progenitors, by contrast, serve a transitory role in theamplification of a cell population during development or regeneration.When the self-renewal capacity of precursors cannot be rigorouslyascertained, investigators sometimes use the terminology“stem/progenitor cells”. The term is used also for cell therapiesinvolving the use of both stem cells and/or progenitors.

Stem cells in the first stages of the developing mammalian embryo, alongwith primordial germ cells at later stages, have the remarkable capacityto give rise to all of the body's cell types, and are therefore termedpluripotent. Embryonic stem (ES) cells remain pluripotent duringextensive expansion as established cell lines. The self-renewalpotential of ES cells appears virtually unlimited, although theaccumulation of spontaneous mutations and chromosomal rearrangementseventually degrades their practical utility. Similarly pluripotent stemcells can be generated through the reprogramming of mature somatic cellsby the introduction of small sets of defined genetic factors, and thecells are termed induced pluripotent stem (iPS) cells.

Mesenchymal stem cells or MSCs can be derived from bone marrow, adiposetissue, umbilical cord tissue, Wharton's Jelly and amniotic fluid, growreadily in culture under ordinary culture conditions, can betransplanted by a vascular route or by grafting, and lineage restrictedto any mesodermal fate (e.g., bone, cartilage, tendon, muscle). They areable to lineage restrict to endodermal or ectodermal fates but withexceedingly low efficiency, so much so that this feature is not ofpractical utility with respect to clinical programs. The usefulness ofMSCs for clinical programs is proving to be primarily by theirproduction of secreted paracrine signals (matrix and soluble factors) orby immune-modulatory mechanisms, findings that have resulted in theiruse in clinical programs world-wide to alleviate liver conditions andpancreatic conditions including diabetes.

TABLE 1 Intrahepatic Lineage-dependent Phenotypic Traits in Human LiversMaturational Early Intermediate Late Lineage Stages (Stages 1-4; zone 1)(Stages 5-6; zone 2) (Stages 7-10; zone 3) Cell sizes 7-9 μm-stem cells~20-25 μm ~25-35 μm 10-12 μm--hepatoblasts 12-15 μm-committedprogenitors 17-18 μm-adult cells Ploidy Diploid Diploid and withTetraploid or higher some tetraploid (depends on age of person)Proliferation Hyperplastic growth Hyperplastic growth Hypertrophicgrowth (DNA synthesis with and with some (DNA synthesis withcytokinesis) hypertrophic growth negligible cytokinesis) (depends on theextent of cytokinesis) Representative Stem Cells: NCAM, Transferrin,P4503A4¹, genes expressed EpCAM, CD44H (no AFP TAT¹, glutathione-S- andlittle to no Fully regulatable transferase¹, albumin), CS-PGs^(1,4)albumin² HP-PGs⁴ Hepatoblasts: Factors associated ICAM-1¹, EpCAM, AFP¹,with apoptosis¹ CD44H, constitutive albumin², P450A7¹, HS-PGs^(1,4)Hepatocytes: enzymes in glycogen synthesis¹, CX 28¹, HS-PGs⁴, partiallyregulatable albumin² Levels of expression are due to lineage-dependentactivation of transcription¹, acquisition of relevant regulatoryelements in transcription², translational mechanism(s)³,posttranscriptional modifications (e.g., in Golgi)⁴ AFP,alpha-fetoprotein; CD44, receptor for hyaluronans; CS-PG, chondroitinsulfate proteoglycan; CX, connexins (gap junction proteins); Cyp450,cytochrome P450s; HS-PG, heparan sulfate proteoglycan; ICAM-1,intercellular adhesion molecule-1; NCAM, neural cell adhesion molecule;TAT, tyrosine aminotransferase

Determined stem cells, commonly called “adult stem cells”, are in fetaland postnatal tissues but are restricted to specific lineages defined bya germ layer (ectoderm, mesoderm, endoderm). Determined stem cells (andtheir descendants, committed progenitors) replenish mature cells thatare lost through normal turnover or injury and disease. Some mature celltypes, such as blood cells and those lining the gut or the outer layerof the skin, have a limited lifespan and must be replaced rapidly. Othermature cells, such as cardiomyocytes and certain neurons, can persistfor years. The proliferation and differentiation of stem cells must beregulated tightly to ensure life-long maintenance of appropriate numbersof specialized cells and of the stem cell compartment itself, undernormal conditions and when cells are replaced because of disease orinjury.

This invention provides a method for delivery of any stem cellpopulation, most especially for determined stem cells or their committedprogenitors, by targeting their delivery by direct injection or bygrafting strategies to the reservoir of stem cell niches giving rise toliver and pancreas. For a discussion of grafting methods and “feedereffects” on stem cell cultures, see U.S. patent application Ser. Nos.12/213,100 and 13/102,939, the disclosures of which are bothincorporated in their entirety herein by reference.

Liver, biliary tree and pancreas are mid-gut endodermal organs centralto handling glycogen and lipid metabolism, detoxification ofxenobiotics, processing of nutrients for optimal utilization, regulationof energy needs, and synthesis of diverse factors ranging fromcoagulation proteins to carrier proteins (e.g., AFP, albumin,transferrin). The integrity of the body depends heavily on liver,biliary tree, and pancreatic functions, and failure in any of them,especially the liver, results in rapid death. In recent years it hasbecome apparent that these tissues comprise maturational lineages ofcells that are in epithelial-mesenchymal cell partnerships. Each lineagetree begins with an epithelial stem cell (e.g., hepatic stem cell)partnered with a mesenchymal stem cell (e.g., an angioblast).

These give rise to cellular descendants that mature coordinately. Thematurational process generates epithelial and mesenchymal cells thatchange step-wise with respect to their morphology, ploidy, growthpotential, biomarkers, gene expression and other phenotypic traits. Thefunctions of the liver and of the pancreas are the net sum of phenotypicproperties of all of the cells throughout the entire maturationallineages. In Table 1 we provide a representative example of this bysummarizing phenotypic properties of parenchymal cells within the liverand at different maturational lineage stages. It is assumed that thereare comparable lineage stages from stem cells or progenitors to maturecells and existing in the pancreas, but these have yet to be definedfully.

The pancreas is located retroperitoneally and provides digestive enzymesto the duodenum and hormones regulating metabolism. The organ isparticularly sensitive to mechanical handling and has a propensity torelease locally its enzymes leading to autolysis. This tendency haslimited the types of surgery that can be done with this organ, includingcell therapy for a pancreatic disease or condition. The liver is lesssensitive to manual manipulation than the pancreas, but access to itrequires abdominal surgery or laparoscopy or access through the biliarytree by endoscopy.

The present invention thus contemplates introducing cells to the liverand to pancreas without physically disturbing or compromising thephysical integrity of these organs.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a method of treatingpancreatic or liver dysfunctions or conditions is provided, the methodcomprising: (a) obtaining a suspension of the stem cells or theirdescendants, committed progenitor cells, respectively; and (b)introducing the suspension into or onto the walls of thehepato-pancreatic common duct—in the case of pancreas—or the walls ofthe biliary tree nearer to the liver—in the case of liver, wherein asubstantial portion of the cells takes residence in the wall, andwherein the cells mature into functional pancreatic or liver cells andmigrate (hypothesized to be by “conveyer belt” mechanisms) to thepancreas or liver, thereby treating the pancreatic or liver dysfunctionor condition, respectively. The cells may be biliary tree stem cells ortheir descendants, committed progenitors, or mesenchymal stem cells forboth liver and pancreas or hepatic stem cells or committed progenitorsfor liver or pancreatic stem cells or their committed progenitors forpancreas. In the future if there is success at controlling ES cells oriPS cells with respect to tumorigenic potential so that they might beused clinically, then they too might be delivered in this way fortreatment of liver or pancreas conditions.

The suspension of cells may be preferably combined with one or morebiomaterials (e.g., collagens, adhesion molecules, proteoglycans,hyaluronans, other glycosaminoglycan chains, chitosan, alginate, andsynthetic, biodegradable and biocompatible polymers, or combinationsthereof), growth factors (e.g., R-spondin, fibroblast growth factors(FGFs), hepatocyte growth factor (HGF), epidermal growth factor (EGF),vascular endothelial cell growth factor (VEGF), insulin like growthfactor I (IGF-1), insulin-like growth factor II (IGF-2), oncostatin-M,leukemia inhibitory factor (LIF), transferrin, insulin, glucocorticoids,growth hormones, estrogens, androgens, thyroid hormones, pituitaryhormones, and combinations thereof), additional cells, or combinationsthereof, to form a graft complex.

The additional cells may comprise the epithelial stem cells and theirmesenchymal partners. For example, biliary tree stem cells (or hepaticstem cells), angioblasts, and precursors to endothelia and stellatecells or combinations thereof, and may be obtained from a portion of thebiliary tree of the subject and that is not diseased or dysfunctionaland/or from the biliary tree of a non-autologous donor. According to themethod, the graft complex (cells+biomaterials+hormones/growth factors)may be introduced by laparoscopic surgery or by endoscopy via injection,by grafting onto the surface of the bile ducts and with a biodegradablecovering around the duct(s), or by a sponge.

In another embodiment of the present invention, a method of repairingthe function of the liver or pancreas in a subject having a pancreas ina diseased or dysfunctional condition is provided, comprising: (a)obtaining a suspension of the stem cells and/or committed progenitorcells; and (b) introducing the suspension to the walls of thehepato-pancreatic common duct—in the case of pancreas—or the walls ofthe bile duct nearer to the liver—in the case of liver, wherein asubstantial portion of the cells introduced take up residence in or onat least a portion of the pancreas or liver as mature pancreatic cellsor liver, respectively, in vivo.

The method is based on an understanding that stem cell populationswithin the biliary tree are the precursors contributing to organogenesisof the liver and pancreas. The lineages of cells begin within stem cellniches, peribiliary glands, and progress to mature cells within theorgans. Peribiliary glands throughout the biliary tree contain cellsthat exhibit phenotypic traits constituting evidence of maturationallineages going from stem cell populations deep within the bile ductwalls (near the fibromuscular layers) to mature cells near the lumens ofthe bile ducts and with proximity either to liver or pancreas. Thesecells have been characterized and show changes in phenotypic traits withproximity to the organ.

The biliary tree is a logical target for transplantation of cells instem cell therapies. There is a network of stem/progenitors organized inmaturational lineages in a radial axis and proximal-to-distal axiswithin the biliary tree and contributing to organogenesis of liver andpancreas throughout life. The advantages of using the biliary tree asthe target site for transplantation are many. The transplantationprocedures can be done as outpatient procedures (e.g. endoscopy) or asminor surgical procedures (laparoscopy). The strategy enables thetransplantation of stem cells or progenitor cells with minimal (if any)immunogenicity and, thereby, provides the potential of avoidingimmunosuppressive drugs for the patients. The procedures involvegrafting strategies, already demonstrated to facilitate engraftment intothe target organ; instead of the approximately 20% engraftment in theliver now documented by many investigators doing cell transplantation bya vascular route, grafting strategies result in nearly 100% engraftment.This avoids ectopic cell distribution, a serious concern in celltransplantation by a vascular route, and optimizes the use of the donorcells (that is avoiding loss of cells from death or from ectopic celldistribution).

The advantages are especially profound for treatment of the pancreas,since its sensitivity to manual manipulation has obviated any chance ofcell therapy directly into the organ. Stem cells transplanted into theportion of the biliary tree near to the pancreas, the hepato-pancreaticcommon duct, overcomes this major difficulty and enables stem celltherapies for the pancreas to become a reality.

DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic of the liver, biliary tree and pancreas showingtheir connection to the duodenum. Intramural and extramural peribiliaryglands (PBGs), the stem cell niches of the biliary tree, are foundthroughout the biliary tree. The intramural PBGs are located in highnumbers within the walls of the bile ducts, from the most interior siteswithin the bile ducts, sites near fibromuscular layers, to the sitesnearest to the bile duct lumens. The cells within the PBGs near thefibromuscular layers are comprised of the highest numbers of cells thatare very primitive (have high levels of pluripotency genes and stem cellgenes and minimal, if any, expression of mature cell genes). Withtransition to the lumens of the bile ducts, (the radial axis ofmaturation) the pluripotency gene expression fades and the expression ofmature cell genes increases.

The numbers of such primitive stem cells are remarkably high throughoutthe biliary tree, with an average of 2-4% of the cells in these PBGs. Inaddition, the PBGs are in high numbers particularly at the branchingpoints of the biliary tree. Shown are some of those sites where thereare high numbers of PBGs (schematically shown with the blue stars). Theextramural PBGs contain primarily very primitive stem cells (high levelsof pluripotency and stem cell genes; negligible levels of mature cellgenes) and are tethered to the surface of the bile ducts by a cord oftissue. The highest number of all of PBGs are found in thehepato-pancreatic common duct near the duodenum, and these contain ˜9%of their cells as the very primitive stem cells. Thus, the biliary treeis a veritable “root system” of stem cells for liver and pancreas.

FIG. 2 is a more detailed schematic of the hepato-pancreatic commonduct. The formation of the liver and pancreas occurs as an outgrowth oftissue from the duodenum at two sites: that which forms the dorsalpancreatic duct; and that which forms the ventral pancreas duct and thebiliary tree leading to the liver. The formation of the intestineresults in a twisting motion swinging the ventral pancreatic duct/andcommon bile duct 180 degrees such that the ventral pancreatic “anlage”,the tissue that will give rise to the ventral pancreas, moves to aposition beneath that of the dorsal pancreas, and the connecting biliarytree are now located on the left side of the duodenum. The mergedhepatic and pancreatic duct are called: “the hepato-pancreatic commonduct.

PBGs within the hepato-pancreatic common duct contain biliary tree stemcells that can give rise to either liver and/or pancreas. It is also thesite of the highest numbers of pancreatic stem cells, descendants frombiliary tree stem cells and with phenotypic traits indicating that theyare now determined stem cells for the pancreas. Although there are alsoa subpopulation of cells qualifying to be hepatic stem cells, thenumbers of those increase with progression along the biliary tree toproximities nearer to the liver. It should be noted that even within theliver, in the large intrahepatic bile ducts, there are PBGs that containa small percentage of cells that are precursors to both liver andpancreas and there are also a small percentage that qualify aspancreatic stem cells and another set qualifying as hepatic stem cells.

FIG. 3 shows representative variations in the connections of thepancreatic duct and bile duct at the ampulla of Vater. One of the mostcommon variations has an interposed septum. There are variations inhumans in how the hepatic and pancreatic ducts merge. This will have abearing in how transplantation into the hepato-pancreatic common ductmight be done. Those in which there is complete fusion of the two (e.g.long and short common channels) will serve as a site forinjection/grafting of the cells. Those in which there is an interposedseptum between the two or when there are wholly separate channels willbe ones requiring transplantation into the relevant one for liver versuspancreas.

FIG. 4 is a flow chart showing a network of stem cell and progenitorcell niches in the Biliary Tree. The stem cell and progenitor cellniches are found throughout the biliary tree and extending into theliver and into the pancreas. The hypothetical start points of theseniches are the Brunner's Glands, found as submucosal glands within theduodenum. These glands are found at no other location within theintestine. Their roles have, in the past, been assumed to be associatedwith facets of functions of the stomach and duodenum. However, themorphological structure and the phenotypic traits of the cells withinthe glands overlap extensively with those of the traits of cells withinthe PBGs.

The PBGS are found throughout the biliary tree. They are found in cysticducts that lead into the gallbladder. Within the gallbladder, there areno PBGS and here we have found that the stem cells and progenitors areorganized differently in that they are localized to crypts (in patternssimilar to crypts within the intestine) and give rise to cells thatmature with progression to the tops of the villi within the gallbladder.

The PBGs within the liver are in the large intrahepatic bile ducts andthese connect anatomically to the ductal plates found in fetal andneonatal livers and that transition to the canals of Hering found inpediatric and adult livers. The PBGs, the ductal plates, and the canalsof Hering contain stem cells and progenitors.

The PBGs in the hepato-pancreatic common ducts near the duodenumtransition to the pancreatic duct glands within the pancreas. With thistransition, the cells convert entirely to committed progenitors. Thus,there are only very rare stem cells within pancreatic ducts orpancreatic duct glands. Rather, the biliary tree stem cells andpancreatic stem cells are localized essentially entirely within the PBGsfound in the hepato-pancreatic common duct or in other portions of thebiliary tree that are independent of the pancreas.

FIG. 5 is a flowchart showing Stem/Progenitor Cell Subpopulations givingrise to Liver, Biliary Tree and Pancreas. There are multiple stem celland progenitor cell subpopulations throughout the biliary tree. Shownare those in the intramural PBGs and those being the precursors toeither liver or pancreas (not shown are those in the gallbladder).Demonstrated are some of the changes in phenotypic traits occurringwithin the radial axis throughout the biliary tree (the first 3 stagesshown). Then shown are those within the hepato-pancreatic common ductwith proximity to the pancreas (the lineages of cells descending fromthe pancreatic stem cells). Alternatively, there are the descendantsfrom the hepatic stem cells found in highest numbers in the PBGs in thelarge intrahepatic bile ducts and transitioning to the ductal plates(fetal or neonatal) or canals of Hering (pediatric or adult). Phenotypictraits common to all of these lineage stages of stem cells andprogenitors are cytokeratin 8 and 18 and sodium iodide symporter (NIS).

FIG. 6 is a schematic of hypothetical lineages along aproximal-to-distal axis starting from the duodenum and ending withmature cells at either liver or pancreas. The radial axis of lineagestages is complemented by a proximal-to-distal axis of lineage stages.Thus, the highest numbers of very primitive stem cells (high levels ofpluripotency gene expression and other stem cell markers) is found inthe hepato-pancreatic common duct near to the duodenum. With progressiontowards the pancreatic ducts, the PBGs increasingly contain higher andhigher percentage of cells with markers indicative of a pancreatic fate;once within the pancreatic duct, there are few, if any, traits of stemcells and only traits of committed progenitors and of intermediates inlineages progressing towards acinar or islet cells. With progressionalong the biliary tree (common duct and then common hepatic duct, etc.)there are increasing percentages of cells within the PBGs with markersindicative of an hepatic fate.

FIG. 7 provides select components of Kubota's Medium and HormonallyDefined Medium. The ability to maintain stem cells and progenitors exvivo has been dependent on establishment of wholly defined, serum freemedia comprised of the essential components required by the cells.Kubota's Medium (KM) was established as a serum-free, wholly definedmedium for ex vivo maintenance of endodermal stem cells and progenitors.It has proven successful for stem cells and progenitors from liver,biliary tree, pancreas and also from lung and, with some modifications,also for intestine. Kubota's Medium does not permit survival of maturecells, only stem cells and progenitors.

Defined media for the mature cells requires supplementation withadditional factors, as noted in the figure, and with specific additionsfor specific adult fates. These are the soluble factors required for thedifferentiation process. For optimal achievement of eitherself-replication for stem cells versus maturation to an adult cell faterequires use of substratum of lineage-stage specific extracellularmatrix components. For self-replication, the matrix components includehyaluronans and forms of proteoglycans with minimal sulfation; formaturity to adult cell states require multiple matrix components,ideally those found in biomatrix scaffolds, matrix extracts derived fromthe adult tissue.

FIG. 8 shows cultures of biliary tree stem cells plated onto plastic andin Kubota's Medium. Under these conditions, there are two majorcategories of biliary tree stem cells that emerge: type 2 cells expressEpCAM on every cells. Type 1 cells do not express EpCAM but acquireexpression of it at the edges of colonies, sites at which they areundergoing slight differentiation. Type 1 cells give rise to type 2cells as shown morphologically in FIG. 8A.

FIG. 9 graphically illustrates the inventive strategy for stem celltherapy of liver or of pancreas using an endoscopic strategy. If thepancreas is being treated, then the graft would be placed within thewalls or patched onto the walls of the hepato-pancreatic common duct. Ifthe liver is being treated, then the endoscope would be moved into thecommon duct and possibly into the common hepatic duct and there graftedinto or onto the wall of the duct.

FIG. 10 is immunohistochemistry of human gallbladder demonstratinglocation of stem cells and progenitors in the crypts.

DETAILED DESCRIPTION OF THE INVENTION

Diabetes is a genetic condition affecting the pancreas and amenable totreatment by cell therapy strategies. (Diabetes is merely arepresentative of a condition that can be treated by the inventivestrategy, but it should be noted, that any liver condition or diseasecan be treated by a similar process.) The global incidence of diabetesmellitus has increased dramatically over the past few years andcontinues to rise. The quest for curative therapies that normalize bloodglucose levels and provide independence from exogenous insulin therapiesimpacts patients with type 1 diabetes (T1D) and a significant subset ofpatients with type 2 diabetes (T2D) who have a functional deficiency ininsulin production. Islet transplantation has been attempted, but theapproach has been constrained by the limited yield of quality donorpancreata that can be utilized to isolate islets. Therefore, attemptshave been made to identify one or more precursor populations that can belineage restricted to islet cells and, thereby, constitute a nearlylimitless and reproducible supply of transplantable and functionalislets.

In the past, determined stem cells for pancreas have not been consideredan option based on the findings that there are only very rare pancreaticstem cells and instead essentially only committed progenitors inpostnatal pancreatic tissue. The committed progenitors in pancreas arefound in the pancreatic ducts, particularly in the pancreatic ductglands (PDGs). The phenotype of these committed progenitors and theiractual contributions to the endocrine compartment of the pancreas remainactively debated, but it is generally agreed that these are the primaryprecursor populations for islets and that are found within the pancreasproper.

Recently, a new source of islet precursors was identified in biliarytrees in donors of all ages. See U.S. patent application Ser. No.12/926,161, the disclosure of which is incorporated herein in itsentirety by reference. The biliary tree has been found to containmultiple subpopulations of determined stem cells with indefiniteexpansion potential in culture and that can mature to hepatocytes,cholangiocytes or islets depending on the microenvironment in vitro orin vivo (it is assumed but not yet shown that the stem cells can giverise also to acinar cells).

Peribiliary glands (PBGs) are stem cell niches found within the walls ofbile ducts throughout the ramifying biliary tree from the duodenum tothe liver and to the pancreas. They occur in high numbers at the branchpoints of the biliary tree and are especially concentrated in the largeintrahepatic bile ducts and in the hepato-pancreatic common duct nearthe duodenum. The PBGs form direct anatomical connections to reservoirsof stem cells within the liver, the ductal plates of fetal and neonatallivers and that transition to canals of Hering of pediatric and adultlivers, and to reservoirs of committed progenitors, the pancreatic ductglands (PDGs), within the pancreas; this network is evident in people ofall ages. The network of niches containing stem cells and/or committedprogenitors, results in a continuous network of stem cells contributingto the formation of liver, biliary tree, and pancreas supporting anhypothesis of ongoing organogenesis of the liver, biliary tree andpancreas throughout life.

The largest numbers of PBGs, those found in the hepato-pancreatic commonduct, connect anatomically to PBGs that transition in their cellularconstituents with progression towards liver or to pancreas. Cells withinthe PBGs morph from homogenous stem cell populations in thehepato-pancreatic common ducts (or the large intrahepatic bile ducts) toones dominated by progenitors having a particular mature cell fate:mature hepatic parenchymal cells versus mature bile duct cells versusmature pancreas cells, depending on the location of the PBGs within theextrahepatic biliary tree.

The transitions occur along two, overlapping axes: a radial axis and aproximal-to distal axis and with progression occurring hypothetically ina “conveyer belt fashion” analogous to that in the intestine. The radialaxis starts with primitive stem cells located in intramural PBGs deepwithin the bile duct walls at sites near the fibromuscular layer andending with mature cells at the lumens of the bile ducts. The radialaxis near the pancreas shows transitions to pancreatic-like cells; thatnear the liver transitions to mature hepatic parenchymal cells; thosein-between, result in mature cells with bile duct traits.

The proximal-to-distal axis progresses from PBGs containing primitivestem cells next to the duodenum and progresses along the length of thebiliary tree to PBGs located within the large intrahepatic bile ductsand thence to canals of Hering within the liver acinus; they contain amix of stem cells and committed progenitors. The maturational processoccurs also from stem cells in PBGs in the hepato-pancreatic common ductnear the duodenum to pancreatic duct glands (PDGs) within the pancreasand that contain only committed pancreatic progenitors. The PBGs nearestto the duodenum contain primitive stem cells that express markers ofpluripotency (Nanog, OCT4, SOX2, SALL4, KLF4), proliferation (Ki67), andearly hepato-pancreatic commitment (SOX17, SOX9, PDX1, LGR5) but do notexpress intermediate markers such as EpCAM or mature markers such asinsulin or albumin. With progression along the maturational axes, thereis fading and then loss of pluripotency genes and proliferation markers,maintenance of SOX9 but loss of PDX1 for the progression towards liver,or loss of SOX 17, for the progression towards pancreas. EpCAM isactivated in cells at intermediate stages of the maturation and goingeither to liver, bile duct, or pancreas. Intermediate markers goingtowards liver include albumin and alpha-fetoprotein (AFP), whereas theones going towards pancreas include NGN 3, MUC 6 and insulin. See FIG.5.

The biliary tree stem cells can be isolated by immunoselection or byculture selection. The markers identified to date and by whichimmunoselection might be done for subpopulations of the biliary treestem cells from cell suspensions of the biliary tree include epithelialcell adhesion molecule (EpCAM), LGR5, NCAM, CD44 (hyaluronan receptor),and CXCR4. For culture selection, the biliary tree tissue is prepared asa cell suspension and then plated onto culture plastic and in serum-freeKubota's Medium. The details of these protocols are given below.

Under expansion conditions, human biliary-tree-derived stem cells(hBTSCs) are able to proliferate for months as undifferentiated cells,whereas precursors derived from pancreas behave as committed progenitorsand undergo only approximately 8-10 divisions but then go throughpartial endocrine differentiation. A hormonally defined medium (HDM)tailored for differentiation of the cells to islets used in combinationwith embedding the cells into mixtures of matrix components foundassociated with islets in vivo results in cell aggregates, spheroids,with ultrastructural, electrophysiological and functionalcharacteristics of neoislets. These neoislets have been able to rescueanimals with a diabetic condition by enabling them to produce insulin.Therefore, peribiliary gland-derived stem cells transition to pancreaticduct gland's committed progenitors as part of ongoing pancreaticorganogenesis throughout life.

The present invention is predicated on an understanding that treatmentsof pancreas, including forms of cell therapy, can be targeted to thehepato-pancreatic common duct and these treatments would modify orregulate cells that give rise to the pancreas. The treatments could bedelivered to the hepato-pancreatic common duct either by laparoscopicsurgery or by endoscopy or by placing the graft as a hydrogel around theoutside of the duct along with a covering forming a cuff around the ductand that is surgically glued to the duct. Once delivered, the cells“mature” and migrate, in a conveyer belt fashion, to the pancreas, wherethey perform “pancreatic” functions, replacing or complimenting thediseased or dysfunctional pancreas. In this way, the pancreas per se isnot disturbed in introducing the cells. Rather, the necessary cells areintroduced “upstream” and allowed to migrate to their native locationwithin the pancreas.

The present invention is directed to grafting technologies that involvethe delivery of transplanted cells as an aggregate on or in scaffoldsthat can be localized to the diseased tissue to promote necessaryproliferation and engraftment. Thus, the invention takes into accountnot only the cell type to be transplanted, but also the cell type incombination with the appropriate biomaterials and grafting method forthe most efficient and successful transplant therapies. Graftingtechnologies of the present invention are translatable to therapeuticuses in patients and provide alternative treatments for regenerativemedicine to reconstitute diseased or dysfunctional tissue. Indeed,although the present application has been largely drafted with diabetesas representative of a strategy for treatment with grafting into thehepato-pancreatic common duct, the strategy is also applicable fortreatment of liver diseases by grafting into the bile duct wall in adifferent region of the biliary tree, one near to the liver.

Cell Sourcing

According to the invention, desired cell populations may be obtaineddirectly from a donor having “normal,” “healthy” tissue and/or cells,meaning any tissue and/or cells that is/are not afflicted with diseaseor dysfunction. Of course, such a cell population may be obtained from aperson suffering from an organ with disease or dysfunction, albeit froma portion of the organ that is not in such a condition. The cells may besourced from any appropriate mammalian tissue, regardless of age,including fetal, neonatal, pediatric, and adult tissue, preferablygallbladder or biliary tissue connected to intact livers and pancreases.

Multipotent human biliary tree stem cells (hBTSCs) are the preferredcells for this inventive method and can be isolated from the gallbladderor any portion of the biliary tree tissue but are found at especiallyhigh numbers in the peribiliary glands and at the branching points ofthe tree, particularly in the hepato-pancreatic common duct or in thelarge intrahepatic bile ducts. In the interest of clarity for thisapplication, the term “Biliary Tree Stem Cell” will be used herein torefer to the inventive mammalian multipotent stem or progenitor cell,cell populations comprising such inventive cells, and cells populationsenriched for the inventive cells. See U.S. patent application Ser. No.12/926,161, the disclosure of which is incorporated herein in itsentirety by reference in this respect.

Human gallbladders do not have peribiliary glands; however, they containa population of stem/progenitor cells within mucosal crypts and withoverlapping features of hBTSCs. Therefore, the term “Biliary Tree StemCells” includes also stem/progenitor cells isolable from humangallbladders. This is an advantage given that removal of the gallbladderis done routinely for many reasons and with minimal negativeconsequences to the patient and allows for autologous cell therapies orallogeneic ones depending on the need of the patient being treated withcell therapy.

Biliary tree stem cells can be differentiated into multiple endodermalfates. Indeed, the stem cells may be induced to differentiate intomature cell types of several endodermal lineages including pancreas orliver. For pancreatic islet cells, the biliary tree stem cells areincubated with a medium that is modified from Kubota's Medium preparedwithout glucocorticoids and then by supplementation with copper(10⁻¹²M), calcium (levels approx. 0.6 mM), 10 ng/ml basic fibroblastgrowth factor (bFGF), 2% B27, 0.1 mM ascorbic acid, 0.25 μM cyclopamine,and 0.5 μM RA (retinoic acid). After 4-5 days, the bFGF is replaced with50 ng/ml exendin-4. The matrix scaffolds for the grafts used arecomprised of 60% type IV collagen and laminin (these two at 1:1 ratio)and 40% hyaluronans, and are also effective with the addition of type VIcollagen and nidogen to the mix of matrix components. One can also usesimple hyaluronans plus the hormonal mix with the understanding that thelineage restriction process will go more slowly than occurs withhyaluronans plus other matrix components.

Cells may also be sourced for different therapies from “lineage-staged”populations based on the therapeutic need. For example, later-stage“mature” cells may be preferred in cases where there is a need for rapidacquisition of functions offered only by the late lineage cells, or ifthe recipient has a lineage-dependent virus that preferentially infectsthe stem cells and/or progenitors such as occurs with hepatitis C orpapilloma virus. In any event, “progenitor” cells may be used toestablish any of the lineage stages of their respective tissue(s). For adiscussion of lineage-staged liver cell populations and method of theirisolation, see U.S. patent application Ser. Nos. 11/560,049 and12/213,100, the disclosures of which are both incorporated in theirentirety herein by reference.

Samples of biliary tree tissue can be dissected surgically from liversor pancreas obtained for and then rejected for transplant due to reasonssuch as steatosis; anatomical abnormality, or major vascular disease; orthey can be obtained from resection material. They can be fromgallbladders removed for various reasons. The tissue is then dividedinto segments and processed further. Segments that are especially richin the biliary tree stem cells include: the large intrahepatic bileducts, the hilum, common hepatic duct, cystic duct, common duct, commonhepato-pancreatic duct and gallbladder. Each part can be furtherdissected into pieces cutting along the longitudinal diameter.

The biliary tree stem cells have been shown to give rise to multipleendodermal fates including liver, biliary tree, and pancreas cells. Asprimitive stem cells, they express pluripotency genes (Nanog, SOX2,KLF4, OCT4, SALL4); hepatic and pancreatic endodermal transcriptionfactors (e.g., SOX17, SOX 9, FOXA2, PDX 1;) and surface markers typicalfor stem cells including LGR5 (leucine-rich repeat-containing G proteincoupled receptor 5), CD44 (hyaluronan receptor), CD133 (prominin);CD56/Neuronal cell adhesion molecule or NCAM); and CXCR4 (CXC-chemokinereceptor 4). As they begin to mature towards a pancreatic or hepaticfate, they acquire expression of CD326/Epithelial cell adhesion moleculeor EpCAM.

Furthermore, with progression in the maturational lineage towards liver,the biliary tree stem cells lose pancreatic markers (e.g., PDX1) andacquire and then steadily increase expression of early lineage markersof the liver such as HNF6, HES1, alpha-fetoprotein (AFP) and albumin).

With maturational progression towards pancreas, the biliary tree stemcells lose hepatic markers (e.g., SOX 17) but not pancreatic ones (e.g.,PDX1) and acquire and then steadily increase expression of early lineagemarkers of the pancreas (e.g., NGN3, MUC6, insulin, amylase). Notably,PDX1 and NGN3 are known to be essential for development of the pancreasand the endocrine pancreas, respectively.

However, the biliary tree stem cells do not express (or only faintlyexpress) markers of mature cells such as the mature markers ofcholangiocytes (e.g., secretin receptor, CFTR, aquaporins), hepatocytes(e.g., tyrosine aminotransferase or TAT, transferrin, or “late” P450ssuch as P450-3A4) or islet cells (e.g., glucagon, somatostatin, highlevels of insulin). They do not express at all markers for mesenchymalcells (e.g., CD146, desmin), endothelial cells (e.g., VEGF receptor,CD31, Van Willebrand Factor) or hemopoietic cells (e.g., CD45). Thepattern of expression of the antigens is stable throughout the life ofthe cultures as long as they are maintained under self-replicationconditions consisting of Kubota's Medium or its equivalent and with asubstratum of culture plastic or hyaluronans.

These phenotypic traits can be determined using endpoint andquantitative (q)-RT-PCR assays and by immunohistochemistry of tissue invivo, of freshly isolated cells, or of cultured cells. The co-expressionin the same cells or in cells within the same peribiliary gland ofmultiple markers of endodermal stem/progenitors (e.g., SOX 9, SOX17,PDX1, NGN3, FOXA2) is a unique and surprising feature that isdistinctive from the findings with respect to embryonic stem (ES) cellsundergoing lineage restriction to pancreas and in which thesetranscription factors are observed sequentially, but not all at the sametime. Furthermore, the expression of these transcription factors isabsent in mature biliary cells at the lumenal surface of the bile ducts.

The biliary tree stem cells of the present invention, as explainedabove, are stem/progenitors giving rise to mature cells of the multipleendodermal tissues including liver, biliary tree, and pancreas.

The stem cell populations from human biliary tree tissue can be isolatedby immunoselection technologies (e.g., flow cytometry, panning, magneticbead isolation). Alternatively, or in addition to immunoselection, thebiliary tree stem cells may be identified and isolated by cultureselection technologies that comprise tissue culturing the cells underspecific conditions. For example, cell suspensions prepared from thebiliary tree tissue may be plated onto plastic or onto (or embedded in)hyaluronans. In other embodiments, the plastic is coated optionally withmatrix components found in embryonic/fetal tissues such as type IIIcollagen or hyaluronans, or combinations thereof.

The medium used for culture selection, serum-free Kubota's Medium or itsequivalent, is strongly selective for the survival and proliferation ofthe biliary tree stem cells and their partner mesenchymal cells,angioblasts and stellate cell precursors, but is not selective formature cells of the biliary tree. The essence of this medium is that itis any basal medium containing no copper, low calcium (<0.5 mM),insulin, transferrin/Fe, free fatty acids bound to purified albumin and,optionally, also high density lipoprotein.

Kubota's Medium or its equivalent is serum-free and contains onlypurified and a defined mix of hormones, growth factors, and nutrients.More specifically, the medium is comprised of a serum-free basal medium(e.g., RPMI 1640 or DME/F12) containing no copper, low calcium (<0.5 mM)and supplemented with insulin (5 μg/ml), transferrin/Fe (5 μg/ml), highdensity lipoprotein (10 μg/ml), selenium (10-10 M), zinc (10-12 M),nicotinamide (5 μg/ml), and a mixture of purified free fatty acids boundto a form of purified albumin. The detailed methods for the preparationof this media have been published elsewhere, e.g., Kubota H, Reid L M,Proceedings of the National Academy of Sciences (USA) 2000;97:12132-12137, the disclosure of which is incorporated herein in itsentirety by reference.

In addition to the cells required to provide the “function” per se of adiseased or dysfunctional internal organ, the graft preferably includesadditional cellular components that preferably mimic the categories ofcells comprising the epithelial-mesenchymal cell relationship, thecellular foundation of all tissues. Epithelial-mesenchymal cellrelationships are distinct at every maturational lineage stage.Epithelial stem cells are partnered with mesenchymal stem cells andtheir maturation is coordinate with each other as they mature to all thevarious adult cell types within a tissue. The interactions between thetwo are mediated by paracrine signals that comprise soluble signals(e.g., growth factors) and extracellular matrix components.

According to one embodiment of the invention, the isolated cellpopulations are combined with known paracrine signals (discussed below)and “native” epithelial-mesenchymal partners, as needed, to optimize thegraft. Thus, the grafts will comprise the epithelial stem cells (e.g.the hepatic stem cells) mixed together with their native mesenchymalpartners (e.g. angioblasts). For a transit amplifying cell niche graft,hepatoblasts can be partnered with precursors to hepatic stellate cellsand/or endothelia. In some grafts one can make a mix of the two sets ofepithelial-mesenchymal partners: hepatic stem cells with angioblasts andhepatoblasts with hepatic stellate cell precursors and endothelial cellprecursors to optimize the establishment of the liver cells in the hosttissue. The microenvironment of the graft into which the cells areseeded will be comprised of the paracrine signals, matrix and solublesignals, that are produced at the relevant lineage stages used for thegraft.

Grafts can also be tailored to manage a disease state. For example, tominimize effects of lineage dependent viruses (e.g., certain hepatitisviruses) that infect early lineage stages and then mature coordinatelywith the host cells, one can prepare grafts of later lineage stage(e.g., hepatocytes and their native partners, sinusoidal endothelialcells) that are non-permissive for viral infection by some viruses.

An example of a stem cell graft, using pancreatic cell therapies as amodel, would comprise the biliary tree stem cells and angioblasts. Incontrast, a graft of “mature” liver cells would comprise hepatocytes,mature endothelial cells and mature stellate cells. For a discussion ofthe epithelial-mesenchymal cell relationship of livers, see U.S. patentapplication Ser. No. 11/753,326, the disclosure of which is incorporatedin its entirety herein by reference.

Grafting Materials

The use of biomaterials according to the invention provides a scaffoldfor cell support and signals that assist in the success of the graftingand regenerative processes. As tissue of solid organs in an organismundergo constant remodeling, dissociated cells tend to reform theirnative structures under appropriate environmental conditions. For adiscussion on grafting methods suitable for application with the presentinvention, see U.S. patent application Ser. No. 13/102,939, thedisclosure of which are both incorporated in their entirety herein byreference.

In all tissues, the paracrine signaling comprises both soluble (myriadgrowth factors and hormones) and insoluble (extracellular matrix (ECM)signals. Synergistic effects between the soluble and (insoluble) matrixfactors dictate growth and differentiative responses by the transplantedcells. The matrix components are the primary determinants of attachment,survival, cell shape (as well as the organization of the cytoskeleton),and stabilization of requisite cell surface receptors that prime thecells for responses to specific extracellular signals.

The ECM is known to regulate cell morphology, growth and cellular geneexpression. Tissue-specific chemistries similar to that in vivo may beachieved ex vivo by using purified ECM components. Many of these areavailable commercially and are conducive to cell behavior mimicking thatin vivo.

Suitable matrix components include collagens, adhesion molecules (e.g.,cell adhesion molecules, tight junctions, basal adhesion molecules),elastins, and carbohydrates that form proteoglycans (PGs) andglycosaminoglycans (GAGs). Each of these categories defines a genus ofmolecules. For example, there are at least 25 collagen types present,each one encoded by distinct genes and with unique regulation andfunctions. The various matrix components that are proteins (e.g.,collagens, attachment proteins) are generally available commercially.Tissue-specific forms of glycosaminoglycans (e.g., tissue-specificheparins) can be purified from natural sources and/or a few can besynthesized. To be sure, the grafts can be successful without theglycosaminoglycans, but may take longer and may not have some of thespecificities that the glycosaminoglycans dictate.

Additional biomaterials that might offer methods of grafting includeinorganic, natural materials like chitosan and alginate as well as manysynthetic, biodegradable and biocompatible polymers. These materials areoften “solidified” (e.g., made into a gel) through methods includingthermal gelation, photo cross-linking, or chemical cross-linking. Witheach method, however, it is necessary to account for cell damage (e.g.,from excessive temperature ranges, UV exposure). For a more detaileddiscussion of biomaterials, specifically the use of hyaluronanhydrogels, see U.S. patent application Ser. No. 12/073,420, thedisclosure of which is incorporated in its entirety herein by reference.

The particular selection of which matrix components may be guided bygradients in vivo, for example, that change from the stem cellcompartment to the late lineage stage cells. The graft biomaterialspreferably mimic the matrix chemistry of the particular lineage stagesdesired for the graft. The efficacy of the chosen mix of matrixcomponents may be assayed in ex vivo studies using purified matrixcomponents and soluble signals, many of which are availablecommercially, according to good manufacturing practice (GMP) protocol.The biomaterials selected for the graft preferably elicit theappropriate growth and differentiation responses required by the cellsfor a successful transplantation.

Concerning the liver, the matrix chemistry associated with the hepaticstem cells is present in the peribiliary glands of the largeintrahepatic bile ducts and in the ductal plates (fetal and neonatallivers) that transition to become the canals of Hering (pediatric andadult livers). The later lineage stages of hepatic parenchymal cells arein the Space of Disse, the area located between the parenchyma and theendothelia or other forms of mesenchymal cells.

In addition to a change in cell maturity within the different zones ofthe liver, a change in matrix chemistries is also observed. The matrixchemistry in the ductal plates or canals of Hering (and potentially theintrahepatic peribiliary glands) is similar to that found in fetallivers and consists of type III and V collagens (no type I collagen),hyaluronans, forms of laminin that bind to alpha6/beta4 integrin (e.g.,laminin 5), and forms of chondroitin sulfate proteoglycans (CS-PGs) thathave minimal sulfation.

This zone transitions to a different matrix chemistry in the regionadjacent to the canals of Hering and associated with hepatoblasts andconsists of type IV, V and VI collagens, hyaluronans, forms of lamininthat bind to alpha/beta1 integrin, more sulfated CS-PGS and weaklysulfated heparan sulfate proteoglycans (HS-PGs).

The transit amplifying cell compartment transitions to yet later lineagestages, and with each successive stage, the matrix chemistry becomesmore stable (e.g., more highly stable collagens), turns over less, andcontains more highly sulfated forms of GAGs and PGs. The most maturecells are associated with forms of heparin-PGs (HP-PGs), meaning thatmyriad proteins (e.g., growth factors and hormones, coagulationproteins) can bind to the matrix and be held stably there via binding tothe discrete and specific sulfation patterns in the GAGs. Thus, thematrix chemistry transitions from its start point in the stem cell nichehaving labile matrix chemistry associated with high turnover and minimalsulfation (and therefore minimal binding of signals in a stable fashionnear to the cells) to stable matrix chemistries with increasing amountsof sulfation (and therefore higher and higher levels of signal bindingheld near to the cells).

Concerning the pancreas, the transitions in matrix chemistry from stemcells to mature cells give rise to distinct chemical compositionsassociated with the acinar cells versus the islets. Among thedistinctions known are that islets are especially rich in forms ofheparan sulfate proteoglycans (glypicans and syndecans), in nidogen, andin network collagens (e.g. type IV, VI), whereas the acinar cells arerich in forms of chondroitin sulfate proteoglycans, fibronectins, andvarious fibrillar collagens. As well, the matrix chemistry associatedwith pancreatic stem/progenitor cells is present in the peribiliaryglands of the hepato-pancreatic duct. Matrices associated with laterlineage stages of pancreatic parenchymal cells are in pancreatic ductsand pancreatic duct glands. Matrices of mature stages include those incontact with pancreatic acinar tissue and pancreatic islet cells.

Hence, the present invention takes into consideration that the chemistryof the matrix molecules changes with maturational stages, with host age,and with disease states. Grafting with the appropriate materials shouldoptimize engraftment of transplanted cells in a tissue, preventdispersal of the cells to ectopic sites, minimize embolization problems,and enhance the ability of the cells to integrate within the tissue asrapidly as possible. Moreover, the factors within the graft can also bechosen to minimize immunogenicity problems.

In the case of human livers or of human biliary tree tissue, cells maybe cultured under serum free conditions. Human hepatic stem cell orhepatoblasts (hHpSC or hHB) can be grafted by themselves, or incombination with angioblasts/endothelial cells. Cells can be suspendedin thiolated and chemically-modified HA (CMHA-S, or Glycosil, GlycosanBioSystems, Salt Lake City, Utah) and in KM (Kubota's Medium) and loadedinto one of the syringes of a set of paired syringes. The other syringemay be loaded with a cross-linker, e.g., poly(ethylene glycol)diacrylate or PEGDA, prepared in KM. The two syringes are coupled by aneedle that flares into two luer lock connections. Thus, the cells inhydrogel and the cross-linker can emerge through one needle to allow forrapid cross-linking of the CMHA-S into a gel upon injection.

The cell suspension in CMHA-S and crosslinker can be either directlyinjected or grafted to the target tissue using a pouch made from tissue(e.g., omentum tissue) or from a synthetic material (e.g., spider silk).Alternatively, the cells may be encapsulated in Glycosil without the useof a PEGDA crosslinker by allowing the suspension to stand overnight inair, leading to disulfide bond crosslinking to a soft, viscous hydrogel.In addition, other thiol-modified macromonomers, e.g., gelatin-DTPH,heparin-DTPH, chondroitin sulfate-DTPH, may be added to give a covalentnetwork mimicking the matrix chemistry of particular niches in vivo. Inanother manifestation, polypeptides containing cysteine or thiolresidues can be coupled to the PEGDA prior to adding the PEGDA to theGlycosil, allowing specific polypeptide signals to be incorporated intothe hydrogel. Alternatively, any polypeptide, growth factor or matrixcomponent such as an isoform of a collagen, laminin, vitronectin,fibronectin, etc., may be added to the Glycosil and cell solution priorto crosslinking, allowing passive capture of important polypeptidecomponents in the hydrogel.

Hyaluronans: Hyaluronans (HAs) are members of one of the 6 largeglycosaminoglycan (GAG) families of carbohydrates, all being polymers ofa uronic acid and an aminosugar [1-3]. The other families comprise thechondroitin sulfates (CS, [glucuronic acid-galactosamine]_(X)), dermatansulfates (DS, more highly sulfated [glucuronic acid-galactosamine]_(X)),heparan sulfates (HS, [glucuronic acid-glucosamine]_(X)), heparins (HP,more highly sulfated [gluronic acid-glucosamine]_(X)) and keratansulfates (KS, [galactose-N-acetylglucosamine]_(X)).

HAs are composed of a disaccharide unit of glucosamine and gluronic acidlinked by β1-4, β1-3 bonds. Biologically, the polymeric glycan iscomposed of linear repeats of a few hundreds to as many as 20,000 ormore of disaccharide units. The HAs have molecular masses typicallyranging from 100,000 Da in serum to as much as 2,000,000 in synovialfluid, to as much as 8,000,000 in umbilical cords and the vitreous.Because of its high negative charge density, HA attracts positive ions,drawing in water. This hydration allows HA to support very compressiveloads. HAs are located in all tissues and body fluids, and most abundantin soft connective tissue, and the natural water carrying capacity lendsitself to speculation to other roles including influences of tissue formand function. It is found in extracellular matrix, on the cell surfaceand inside the cell.

Native forms of HA chemistry are diverse. The most common variable isthe chain length. Some are high molecular weight due to having longcarbohydrate chains (e.g., those in the coxcomb of gallinaceous birdsand in umbilical cords) and others are low molecular weight due tohaving short chains (e.g., from bacterial cultures). The chain length ofHAs plays a key role in the biological functions elicited. A lowmolecular weight HA (below 3.5×104 kDa) may induce the cytokine activitythat is associated with matrix turnover and is shown to be related toinflammation in tissues. A high molecular weight (above 2×105 kDa) mayinhibit cell proliferation. Small HA fragments, between 1-4 kDa, havebeen shown to increase angiogenesis.

Native forms of HA have been modified to introduce desired properties(e.g., modification of the HAs to have thiol groups allowing the thiolto be used for binding of other matrix components or hormones or fornovel forms of cross-linking). Also, there are forms of cross-linkingthat occur in nature (e.g., regulated by oxygen) and yet others thathave been introduced artificially by treatment of native and modifiedHAs with certain reagents (e.g., akylating agents) or, as noted above,establishment of modified HAs that make them permissive to unique formsof cross-linking (e.g., disulfide bridge formation in the thiol-modifiedHAs).

According to the invention, thiol-modified HAs and in situ polymerizabletechniques used for them are some of the forms that are preferred. Thesetechniques involve disulfide crosslinking of thiolated carboxymethylatedHA, known as CMHA-S or Glycosil. For in vivo studies, HA with lowermolecular weight, e.g., 70-250 kDa, can be used, since the crosslinking,either disulfide or PEGDA, creates a hydrogel of very high molecularsize. A thiol-reactive linker, polyethylene glycol diacrylate (PEGDA)crosslinker, is suitable for both cell encapsulation and in vivoinjections. This combined Glycosil-PEGDA material crosslinks through acovalent reaction and in a matter of minutes, is biocompatible andallows for cell growth and profileration.

The hydrogel material, Glycosil, takes into account the gel propertiesconducive to tissue engineering of stem cells in vivo. Glycosil is partof the semi-synthetic extracellular matrix (sECM) technology availablefrom Glycosan Biosciences in Salt Lake City, Utah (now a subdivision ofBiotime in Alameda, Calif.). A variety of products in the Extracel andHyStem trademarked lines are commercially available. These materials arebiocompatible, biodegradable, and non-immunogenic.

Furthermore, Glycosil and Extralink can be easily combined with otherECM materials for tissue engineering applications. HA can be obtainedfrom many commercial sources, with a preference for bacterialfermentation using either Streptomyces strains (e.g., Genzyme, LifeCore,NovaMatrix, and others) or bacterial-fermentation process using Bacillussubtilis as the host in an ISO 9001:2000 process (unique to Novozymes).

The ideal ratios of the cell populations should replicate those found invivo and in cell suspensions of the tissue. A mix of cells allows formaturation of progenitor cells and/or maintenance of the adult celltypes concomitant with the development of requisite vascularization. Inthis way, a composite microenvironment using hyaluronans as a base for acomplex containing multiple matrix components and soluble factors anddesigned to mimic specific micro-environmental niches comprised ofspecific sets of paracrine signals produced by an epithelial cell and amesenchymal cell at a specific maturational lineage stage is achieved.See U.S. patent application No. 61/332,441, the disclosure of which isincorporated herein in its entirety by reference.

The microenvironment of a stem cell niche in the liver consists of theparacrine signals between the hepatic stem cell and angioblasts. It iscomprised of hyaluronans, type III collagen, specific forms of laminin(e.g., laminin 5), a unique form of chondroitin sulfate proteoglycan(CS-PG) that has almost no sulfation and a soluble signal/mediumcomposition close to or exactly that of “Kubota's Medium”, a mediumdeveloped for hepatic stem/progenitors. No other factors are strictlyrequired, though effects can be observed by supplementation with stemcell factor, R-spondin, leukemia inhibitory factor (LIF), and/or certaininterleukins (e.g., IL 6, IL11 and TGF-β1). The stem cell niche form ofCS-PG is not yet available

The transit amplifying cell microenvironment in the liver ismorphologically between that of the hepatoblasts and hepatic stellatecell precursors or endothelial cell precursors. The components of thismicroenvironment include hyaluronans, type IV collagen, specific formsof laminins that bind to αβ1 integrins, more sulfated CS-PGs, forms ofheparan sulfate-proteoglycans (HS-PGs), and soluble signals that includeepidermal growth factor (EGF), hepatocyte growth factor (HGF), stromalcell-derived growth factor (SGF), and retinoids (e.g., vitamin A).

Transplantation Methods

Injectable grafts have an advantage in that they can fill any deficitshape or space (e.g., damaged organs or tissues). According to thismethod, cells are co-cultured and delivered in a cell suspensionembedded in gelable biomaterials, which solidify in situ using variouscrosslinking methods. The suspension may be directly delivered to thewalls of the hepato-pancreatic common duct either by endoscopy or bylaparoscopy or as a patch in cuff-shape around the duct and containingthe hydrogel placed against the outside wall of the duct. They can beimmobilized in the wall by providing a cross-linker, PEGDA, that willcause the hyaluronan-matrix mixture to gel. The procedure should be ableto be done reasonably rapidly and with minimal morbidity to patients.

Direct Injection into the Bile Duct Wall. The fibromuscular walls of thehepato-pancreatic common duct are composed of layers of muscular andconnective tissues that adhere to and envelope the epithelial structuresof the hepato-pancreatic common duct. These layers of fibromusculartissue form a sleeve that extends from the opening of the ampulla ofVater to the separation of the common bile duct and the duct of Wirsung.Separate structures of fibromuscular tissues continue along these twostructures. Fibromuscular walls are embedded in the parenchymal tissueof the head of the pancreas, or in fibro-adipose tissue, depending onanatomical variations and age of the individual.

Patch graft onto the surface of the Bile Duct Wall. Alternatively, thegraft of the stem/progenitor cells admixed within appropriatebiomaterials and with relevant soluble signals can be placed within acovering (e.g. spider silk, omentum) that is surgically glued to thebile duct or around the bile duct (that is as a cuff encircling theduct). The graft of stem cells will interact with the extramuralperibiliary glands tethered to the surface of bile ducts. Thus, thegrafted stem/progenitors can be being incorporated into the duct throughthe outside of the duct.

Both laparoscopic surgery or endocoscopic delivery can utilize anintraluminal approach. Briefly, an endoscope could be inserted throughthe mouth and threaded through the stomach to the duodenum. Using asideport on the endoscope, one can enter into the hepato-pancreaticcommon duct through the ampulla. The hepato-pancreatic common duct wouldbe used for the site of delivery of cells intended for the pancreas. Theendoscope could be moved along the bile duct to reach a site near theliver for delivery of cells targeting the liver. Using this approach,one can transplant the cells as a graft into the periductal region; thegrafting strategy should facilitate the engraftment of the cells. Theprocedure would have to be performed under general sedation.

In laparoscopic surgery, a patient undergoes general anesthesia andsmall incisions (typically less than 1 cm) are made in the skin andfascia to allow placement of laparoscopic ports and instruments. Acamera is introduced into the peritoneal cavity to allow visual guidanceand other instruments including an ultrasound can also be introducedinto the abdomen. These visual techniques provide a means to identifythe pancreas and its parenchymal features including the pancreatic duct.Through ultrasound or other imaging guidance, a surgeon directs a smallgauge needle into the preferred location of the pancreas for delivery ofthe cells. This approach allows the surgeon to identify and controlbleeding, minimize inadvertent delivery or injury to surrounding organsand to provide a mechanism to minimize morbidity associated with theintervention.

Injection may also be performed, for example, using a double barreledsyringe as described hereinabove. Briefly, the cell-matrix-mediummixture is loaded into one side of the syringe with connecting needle tothe other syringe containing the cross-linker PEGDA. The mixture can beinjected through a 25 gauge needle directly into hepato-pancreaticcommon duct and instantly cross-linked to form a hydrogel. The use ofCMHA-S with PEGDA at pH 7.4 allows cell encapsulation as well asinjection in vivo, since the crosslinking reaction occurs over a 1-2 mintime frame.

Inorganic, natural materials like chitosan, alginate, hylauronic acid,fibrin, gelatin, as well as many synthetic polymers can suffice asbiomaterials for injections. These materials are often solidifiedthrough methods including thermal gelation, photo cross-linking, orchemical cross-linking. The cell suspension may also be supplementedwith soluble signals or specific matrix components. Since these graftscan be relatively easily injected into a target area, there is no (orminimal) need for invasive surgery, which reduces cost, patientdiscomfort, risk of infection, and scar formation. CMHA may also be usedfor injectable material for tissue engineering due to its long-lastingeffect while maintaining biocompatibility. Cross-linking methods alsomaintain the material biocompatibility, and its presence in extensiveareas of regenerative or stem/progenitor niches make it an attractiveinjectable material.

In some embodiments, a graft may be designed for placement directly ontoa surface of the walls of the hepato-pancreatic common duct, in whichcase the graft would be held in place with a biocompatible andbiodegradable covering (“band aid”). The cells so delivered should giverise to descendants that can migrate into the pancreas to correct thediseased or genetic condition. If there is difficulty for the migrationto occur through the bile duct surface, then the surface can be abradedchemically or surgically to allow access.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. All publications, patentapplications, patents, and other references mentioned herein areincorporated by reference in their entirety. In case of conflict, thepresent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and notintended to be limiting.

The invention now will be described in particularity with the followingillustrative examples; however, the scope of the present invention isnot intended to be, and shall not be, limited to the exemplifiedembodiments below.

EXAMPLE 1 Example of Efficacy of Grafting Strategy using HyaluronanGrafts

Mouse hepatic progenitor cells were isolated from a host C57/BL6 mouse(4-5 weeks) according to reported protocols. For the “grafting” studies,a GFP reporter was introduced into the hepatic progenitor cells. Thecells were then mixed with hyaluronan (HA) hydrogels and the HAcrosslinked prior to introduction into a subject mouse. Forintroduction/transplantation, mice were anesthetized with ketamine(90-120 mg/kg) and xylazine (10 mg/kg), and their abdomens were opened.The cells, with or without HA, were then slowly injected into the liver.The incision site was closed and animals were given 0.1 mg/kgbuprenorphine every 12 hrs for 48 hrs. After 48 hrs, animals wereeuthanized, and tissue was removed, fixed, and sectioned for histology.

To determine cell localization within the murine models, “control”hepatic progenitor cells were infected for 4 hrs at 37° C. with aluciferase-expressing adenoviral vector at 50 POI. Survival surgery wasperformed as described above, and cells (1-1.5E6) were injected into theliver lobe by a vascular route (hepatic artery or portal vein) or intothe hepato-pancreatic common duct by direct injection or by grafting.Just prior to imaging, mice were injected subcutaneously with luciferin,producing a luminescent signal by the transplanted cells. Using an IVISKinetic optical imager, the localization of cells within the mice wasdetermined Experimental hosts were injected with cells suspended inbuffer with HA.

At 24 hrs, “control” cells injected without HA grafting were found bothin the liver and lung. At 72 hrs, however, most cells could not belocated with only a few identifiable cells remaining in the liver. Thegrafted cells according to the invention, by contrast, were observed asa group of cells successfully integrated into the liver at both 24 and72 hrs, and remained present even after two weeks. Cells transplantedvia this stem cell niche graft were also seen to localize almostexclusively to liver tissue and were not found in other tissues byassays on randomized histological samples.

EXAMPLE 2 Pancreatic Stem Cells

Wang, et al., Stem Cells. 2013; 31(9):1966-1979, incorporated herein itits entirety by reference. Proximal (PBGs)-to-distal (PDGs) maturationallineages start near the duodenum with cells expressing markers ofpluripotency (NANOG, OCT4, SOX2), proliferation (Ki67), self-replication(SALL4), and early hepato-pancreatic commitment (SOX9, SOX17, PDX1,LGR5), transitioning to PDG cells with no expression of pluripotency orself-replication markers, maintenance of pancreatic genes (PDX1), andexpression of markers of pancreatic endocrine maturation (NGN3, MUC6,insulin). Radial-axis lineages start in PBGs near the ducts'fibromuscular layers with stem cells and end at the ducts' lumens withcells devoid of stem cell traits and positive for pancreatic endocrinegenes.

Biliary tree-derived cells behave as stem cells in culture underexpansion conditions, culture plastic and serum-free Kubota's Medium,proliferating for months as undifferentiated cells, whereaspancreas-derived cells underwent only ˜8-10 divisions, then partiallydifferentiated towards an islet fate. Biliary tree-derived cells provedprecursors of pancreas' committed progenitors. Both could be driven by3-dimensional conditions, islet-derived matrix components and aserum-free, hormonally defined medium for an islet fate (HDM-P), to formspheroids with ultrastructural, electrophysiological and functionalcharacteristics of neoislets, including glucose regulatability.Implantation of these neoislets into epididymal fat pads ofimmuno-compromised mice, chemically rendered diabetic, resulted insecretion of human C-peptide, regulatable by glucose, and able toalleviate hyperglycemia in hosts. The biliary tree-derived stem cellsand their connections to pancreatic committed progenitors constitute abiological framework for life-long pancreatic organogenesis

EXAMPLE 3 Stem Cells in the Gallbladder

Gallbladders were obtained from organ donors and laparoscopic surgeryfor symptomatic cholelithiasias. Tissues or isolated cells werecharacterized by immunohistochemistry and flow cytometry.EpCAM+(Epithelial Cell Adhesion Molecule) cells were immunoselected bymagnetic microbeads and plated onto plastic in self-replicationconditions and subsequently transferred to distinct serum-free,hormonally defined media tailored for differentiation to specific adultfates. In vivo studies were conducted in an experimental model of livercirrhosis.

Results: the gallbladder does not have peribiliary glands, but it hasstem/progenitors organized instead in mucosal crypts. These can beisolated by immune-selection for EpCAM. Approximately 10% of EpCAM+cellsin situ and of immunoselected EpCAM+cells co-expressed multiplepluripotency genes and various stem cell markers; other EpCAM+cellsqualified as progenitors. Single EpCAM+cells demonstrated clonogenicexpansion ex vivo with maintenance of stemness in self-replicationconditions. Freshly isolated or cultured EpCAM+cells could bedifferentiated to multiple, distinct adult fates: cords ofalbumin-secreting hepatocytes, branching ducts of secretinreceptor+cholangiocytes, or glucose-responsive,insulin/glucagon-secreting neoislets. EpCAM+cells transplanted in vivoin immune-compromised hosts gave rise to human albumin producinghepatocytes and to human cytokeratin7+cholangiocytes occurring in highernumbers when transplanted in cirrhotic mice. Thus, human gallbladderscontain easily isolatable cells with phenotypic and biologicalproperties of multipotent, endododermal stem cells.

EXAMPLE 4 Net Sum of Analyses Demonstrating Maturational Lineages InSitu

Cells in peribiliary glands at varying site within the biliary tree orin gallbladders were evaluated for expression of pluripotency genes,stem cell genes, and genes of mature liver or pancreas. The expressionof these genes formed a pattern indicative of maturational lineages in aradial axis and proximal-to-distal axis. A summary of this is given inTable 2. The cells within the peribiliary glands nearest to thefibromusular layer were found to be the most primitive having highlevels of expression of pluripotency genes (e.g. SALL4, OCT4, SOX2,KLF4, NANOG), of endodermal stem cell traits (e.g SOX9, SOX17, PDX1,LGR5), and with minimal (if any) expression of mature cell markers(albumin, insulin, CFTR). With progression towards the bile duct lumens,the pluripotency gene expression faded and there was gradual acquisitionof markers for mature cell fates. If the cells were in PBGs near to thepancreas, the mature markers were insulin and other islet hormones oramylase and other markers of acinar cells. If the cells were in PBGsnear to the liver, the mature markers were albumin, transferrin, P450genes and other markers of hepatoacytes or CFTR, secretin receptor andother mature markers of cholangiocytes.

TABLE 2 Comparison of Markers of Stem/Progenitor Cells in Liver, BiliaryTree and Pancreas Example demonstrating maturational lineages in situwithin the biliary tree Proximal-to-Distal Axis of the MaturationalLineages LIVER

PANCREAS Cells Hepatoblasts -- Hepatic Stem Biliary Tree Stem CellPancreatic adjacent to Cells -- Subpopulations in Peribiliary committedCanals of in Canals of glands (PBGs) progenitors Hering Hering ENREF 8ENREF 8 ENREF 8 in Pancreatic Duct ENREF 8 Glands (PDGs) [subpopulationsof these are also in gallbladders but there are found in crypts, notperibiliary glands) Endodermal SOX 9+ SOX 9+ SOX 9+, SOX 9+ 2. SOX 9+,SOX 9+, PDX1+ Markers SOX 17+ SOX 17+ SOX 17+ PDX1+ LGR5+ LGR5+ PDX1+LGR5+ Epithelial CK 8 and 18+, CK19+, E-cadherin+ E-cadherin-, markersCK8, 18, 19+ CAM αβ1 integrin, α6β4 integrin, NCAM, NCAM NCAM, IntegrinsICAM-1, NCAM, EpCAM EpCAM EpCAM EpCAM EpCAM Integrins not yet studiedPluri-potency Negative Moderate levels of Strong expression of OCT4A,Negative genes OCT4, NANOG, SOX2, NANOG, KLF4, SALL4 KLF4, SALL4 OtherStem Weak CXCR4, Strong CXCR4, Strong CXCR4, CD133 CXCR4, CD133, CellMarkers CD133 CD133, CD117 CD24 Hedgehog Weak Indian Strong Indian andStrong Sonic and Indian Hedgehog+ Weak Sonic Proteins and Sonic Sonic³⁰Matrix Laminin**, Laminin**, type III Not yet studied Fetal islets haveproteins type IV collagen Collagen IV, V, VI, collagen Nidogen, Elastin;fetal acinar cells have primarily fibrillar collagens, fibronectinGAG/PGs HS-PGs HA+, CD44+, HA+, CD44+; Others not yet tested Fetalislets have including Minimally sulfated syndecans (HS-PG-1 syndecans,and CS-PGs and glypicans; fetal CS-PGs acinar cells have primarilyCS-PGs Liver traits Albumin++, Albumin ±, AFP- Albumin±, None None NoneAFP+++, AFP- P450A7, Glycogen Pancreatic None None None ISL1, PROX 1,NGN3, MAFA, Traits NeuroD, PAX4 MUC6, Nkx6.1/ NGN3, MUC6± NKx6.2 (Nkx6)and Ptf1a, GLUT2 MDR MDRI- MDR-1+, ABCG2++ Negative ABCG2+ MesenchymalNegative for CD31, CD34, CD45, CD90, CD146, CD105 Cell Traits **Thelaminin associated with the hepatic stem cells binds to alpha6/beta4integrin (laminin-5); that associated with the hepatoblasts binds toalpha/beta1 integrin (laminin-111). The very primitive biliary tree stemcells found within bile ducts and near the fibromuscular layer do notexpress EpCAM or LGR5; those markers occur on cells that areintermediates in the process of becoming either hepatic or pancreaticstem cells. PBGs = peribiliary glands; PDGs = pancreatic duct glands; HA= hyaluronans; HS-PGs = heparan sulfate proteoglycans; CS-PGS =chondroitin sulfate proteoglycans; Syndecans = HS-PGs that havetransmembrane core proteins; Glypicans = HS-PGs linked to plasmamembrane by phosphotidyl inositol (PI) linkages; MDRI = multidrugresistance genes; ²these biliary tree stem cells are the most primitiveand found near the fibromuscular layer within the bile ducts; they giverise in the radial axis maturational lineage to EpCAM+ cells.³Pluripotency genes = OCT4, NANOG, KLF4, SOX2, SALL4. CD117 is found incanals of Hering and present on angioblasts that are tightly bound tothe epithelial stem cells; it is hypothesized to be found in theperibiliary glands in association with the various stem cellsubpopulations. Hepatoblasts, transit amplifying cells, giving rise tohepatocytic and biliary committed progenitors that do not express SOX17,pluripotency genes, LGR5, or other markers of stem cells.

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodifications and this application is intended to cover any variations,uses, or alterations of the invention following. In general, theprinciples of the invention and including such departures from thepresent disclosure as come within known or customary practice within theart to which the invention pertains and as may be applied to theessential features hereinbefore set forth and as follows in the scope ofthe appended claims.

We claim:
 1. A method of treating a pancreatic dysfunction or condition,comprising: (a) obtaining a suspension of stem/progenitor cells; and (b)introducing the suspension into or onto the walls of the biliary tree ina subject having a pancreatic dysfunction or condition, such that asubstantial portion of the cells takes residence in the wall of thebiliary tree, wherein the cells mature into functional pancreatic cellsand migrate to pancreas, thereby treating the pancreatic dysfunction orcondition.
 2. The method according to claim 1, in which the pancreaticprogenitor cells are biliary tree stem cells or pancreatic stem cells orcommitted progenitors derived from the stem cells.
 3. The methodaccording to claim 1, in which the suspension is combined with one ormore biomaterials to form a matrix complex.
 4. The method according toclaim 3, in which the one or more biomaterials comprise collagens,adhesion molecules, proteoglycans, hyaluronans, glycosaminoglycanchains, chitosan, alginate, and synthetic, biodegradable andbiocompatible polymers, or combinations thereof.
 5. The method accordingto claim 1, in which the suspension is combined with hormones, growthfactors, cytokines, additional cells, or combinations thereof.
 6. Themethod according to claim 5, in which the growth factors can include oneor more of the fibroblast growth factors (FGFs), R-spondin, hepatocytegrowth factor (HGF), epidermal growth factor (EGF), vascular endothelialcell growth factor (VEGF), insulin like growth factor I (IGF-1),insulin-like growth factor II (IGF-2), oncostatin-M, leukemia inhibitoryfactor (LIF), transferrin, insulin, glucocorticoids, growth hormones,estrogens, androgens, thyroid hormones, pituitary hormones, andcombinations thereof.
 7. The method according to claim 5, in which theadditional cells comprise biliary tree stem cells, angioblasts, andprecursors to endothelia and stellate cells or combinations thereof. 8.The method according to claim 1, in which the cells are obtained from aportion of the biliary tree of the subject that is not diseased ordysfunctional.
 9. The method according to claim 1, in which the cellsare obtained from the biliary tree of a non-autologous donor.
 10. Themethod according to claim 1, in which the suspension is introduced bylaparoscopic surgery or by endoscopy.
 11. The method according to claim1, in which the suspension of cells is introduced via injection, a graftcomplex with a biodegradable covering, or sponge.
 12. A method ofrepairing the function of a pancreas in a subject having a pancreas in adiseased or dysfunctional condition, comprising: (a) obtaining asuspension of the stem/progenitor cells; and (b) introducing thesuspension into or onto the walls of the hepato-pancreatic common ductof the subject, such that a substantial portion of the cells introducedtake up residence in or on at least a portion of the pancreas as maturepancreatic cells in vivo.
 13. The method according to claim 12, in whichthe pancreatic progenitor cells are biliary tree stem cells orpancreatic stem cells or committed progenitors derived from the stemcells.
 14. The method according to claim 12, in which the suspension iscombined with one or more biomaterials to form a matrix complex.
 15. Themethod according to claim 14, in which the one or more biomaterialscomprise collagens, adhesion molecules, proteoglycans, hyaluronans,glycosaminoglycan chains, chitosan, alginate, and synthetic,biodegradable and biocompatible polymers, or combinations thereof. 16.The method according to claim 12, in which the suspension is combinedwith hormones, growth factors, cytokines, additional cells, orcombinations thereof.
 17. The method according to claim 16, in which thegrowth factors can include one or more of the fibroblast growth factors(FGFs), R-spondin, hepatocyte growth factor (HGF), epidermal growthfactor (EGF), vascular endothelial cell growth factor (VEGF), insulinlike growth factor I (IGF-1), insulin-like growth factor II (IGF-2),oncostatin-M, leukemia inhibitory factor (LIF), transferrin, insulin,glucocorticoids, growth hormones, estrogens, androgens, thyroidhormones, pituitary hormones, and combinations thereof.
 18. The methodaccording to claim 16, in which the additional cells comprise biliarytree stem cells, angioblasts, and precursors to endothelia and stellatecells or combinations thereof.
 19. The method according to claim 12, inwhich the cells are obtained from a portion of the biliary tree of thesubject that is not diseased or dysfunctional.
 20. The method accordingto claim 12, in which the cells are obtained from the biliary tree of anon-autologous donor.
 21. The method according to claim 12, in which thesuspension is introduced by laparoscopic surgery or by endoscopy. 22.The method according to claim 12, in which the suspension of cells isintroduced via injection, a graft complex with a biodegradable covering,or sponge.